The present invention relates to a terminal controller and particularly to a terminal controller in which a control system is incorporated to enable to use a video data terminal from a plurarity of programs by spliting the video screen of the video data terminal.
In recent years, it has been a common practice to utilize a network configuration in which a plurality of computer systems are linked with each other. For example, there is known a laboratory automation (LA) control system comprising hierachically linked host machines (large-scale computers) and local machines (small-scale computers).
The system network configuration aims at:
(1) effective communication resource utilization,
(2) distribution of communication system functions,
(3) flexible expansion of communication network, and
(4) labor saving in application systems.
The virtual telecommunication access method (VTAM) has been known as a method for accessing other machines through communication lines and provides the following advantages: (1) a plurality of terminals can share a communication line, (2) application programs in any host machine can be used at any location in the communication network, and (3) the application programs need not perceive the network configuration. For system network configurations and VTAM, refer to the IBM System Journal, Vol. 15, No. 1, 1976; an article entitled "Synchronous data link control: A perspective", IBM Systems Journal, Vol. 13, No. 2, 1974 and "VOS3 ECS/VTAM Guide" (manual of Hitachi Ltd.) 8080-3-140, 1980.
FIG. 1 illustrates an example of the system network configuration. The host machines 1 and 2 are linked with each other via a communication line through the communication control computers 3 and 4. The communication control computers 3 and 4 can be connected in parallel to a plurality of other machines in the network. A local machine (subhost machine) 5 is linked with the communication control computer 3 of the host machine 1 or with other local machines through a controller 6 which enables data communication between these devices. The controller 6 is provided to control communication procedures such as the high-level data link control (HDLC) procedure and the synchronous data link control (SDLC) procedure.
In the system network configuration, application programs in the host machine 1 can be used from a terminal 7 of the host machine 1 and also from a terminal 8 of the host machine 2. Assuming that a time sharing system (TSS) is used as the application program, a user program (TSS-AP) 9 runs under control of a TSS control program 10 and the TSS control program 10 utilizes a VTAM program 11 in the host machine 1.
To output a message from the user program 9 to the terminal 7 or 8, the HDLC procedures are processed by a network control program 13 in the communication control computer 3 through processing of the VTAM 11 and a host operating system 12; and the message is output to the terminal 7 or it is delivered to the communication control computer 4 to be transmitted to the terminal 8. On the contrary, the above-mentioned processing need only be reversed to input a message from the terminal 7 or 8.
Furthermore, application programs of the host machines 1 and 2 can be accessed from a terminal connected to the local machine 5. The local machine 5 is called a local machine or terminal controller having a cluster control function.
In the local machine 5, a Hitachi network architecture subhost communication program (HICOP) 18 runs under control of an operating system 17, further a data stream compatibility (DSC) program 19 operates under the HICOP 18. The HICOP 18 is provided to carry out VTAM functions, whereas the DSC program 19 is used to enable a terminal 16 connected to the local machine 5 to be treated in the same way as for the terminal 7 connected to the host machine 1 when an input/output message is output to the terminal 16 from the application program 9 in the host machine 1. This means that the functions of terminal controllers are carried out by the local machine 5 and the control programs 17-19. For the data streams between the host machine 1 and the local machine 5 and processing procedures of the HICOP 18 and the DSC program 19, refer to the co-pending U.S. patent application Ser. No. 515,193 filed on July 19, 1983, which corresponds to the Japanese Patent Application No. Sho 57-126341.
As explained above, the system network depicted in FIG. 1 provides the following advantages by use of the VTAM and the cluster control function of the local machine 5: (1) terminals connected to local machines can be utilized as host machine terminals and (2) host machine capability and resources can be used from local machine terminals.
Reference numeral 20 in FIG. 1 indicates a laboratory of a laboratory automation (LA) system including hierarchically connected host machine 1 and local machine 5. The local terminal 16 and a measuring instrument standard interface bus 21 are equipped in the laboratory 20. An application program 23 (to be denoted as LAAP 1) and the like are used to control measuring instruments and apparatuses 22 and to gather measured data in the local machine 5, then the collected data is stored in a local file 24.
In general, the host machine 1 is utilized to perform more precise analyses on the collected data. The U.S. patent application Ser. No. 515,193 has disclosed a control system which allows to use the terminal 16 connected to a local machine as a control terminal for the application program 9 of the host machine 1 and enables the host machine 1 to directly access the local file 24, including effects of the control system.
When only the video terminal 16 is connected to the local machine 5, the operator uses the terminal 16 as a control terminal for the application program 23 to gather measured data, then the terminal 16 is used as a control terminal for the application program 9 of the host machine 1 (, which is called an expansion to a host TSS). That is, the terminal 16 is logically separated from the application program 23 after the local program 23 of the local machine 5 is finished and the terminal operates as a terminal of the host TSS. This means that the terminal 16 is logically connected to the HICOP 18 and DSC 19. Consequently, collection of the measured data by use of the application program and analysis by means of the application program 9 in the host machine 1 cannot be concurrently carried out from a terminal.
Although the measurement and analysis can be naturally conducted by using a terminal for controlling collection of measured data and a terminal for analyzing data by a host machine, the number of expensive terminals is increased and the space for the LA system in the laboratory is reduced. Moreover, the operation becomes complex because only one operator must handle two terminals.
Furthermore, if it is necessary to execute a plurality of application programs from a video terminal, that is, if the outputs from several application programs are to be split and displayed on the screen of a video terminal, all programs that run simultaneously must be regenerated so that the video terminal can be commonly used among them for the following reasons:
(1) The common use of a video terminal must be perceived when each application program manages the buffer for storing the output data stream, and
(2) Each application program must be provided with a processing for determining the destination application program to which a data item input from the video terminal is to be input.
These modifications for existing application programs will necessitate a tremendous time and cost.